氢氧焰燃烧合成纳米二氧化钛颗粒及其分散行为

采用氢氧焰燃烧法合成分散均匀、团聚程度低的纳米TiO2颗粒,采用离子型共聚物改性剂处理制备分散稳定、黏度低的纳米TiO2水性分散体系,借助X射线衍射、比表面积、红外光谱、透射电镜和zeta电位分析等手段,研究纳米TiO2颗粒的晶相、形貌、粒径分布及表面电荷。结果表明:燃烧嘴中心环氢气含量、分散剂用量及pH值对纳米TiO2团聚程度影响较大,当氢气流量控制在1.52 m3/h、水性体系分散剂的质量分数为7.5%、pH控制在8时,纳米TiO2分散性能最佳。     

磷酸锆碟片粒径对提高二氧化钛悬浮液分散稳定性的影响

制备纳米二氧化钛(TiO_2)分别和729.6,1 004.5,1 168.5nm 3种粒径的磷酸锆碟片(ZrP)混合纳米悬浮液,研究了混合悬浮液的分散稳定性。运用稳定性性分析仪,沉降实验和紫外-可见分光光度计综合分析了纳米悬浮液的分散稳定性,并测量了混合悬浮液的粘度。结果表明,加入ZrP碟片后,TiO_2悬浮液的粘度增大,稳定性提高;3种混合纳米悬浮液的粘度相近,但ZrP粒径最小的混合悬浮液,其分散稳定性最好。通过分析发现,3种混合纳米悬浮液中,ZrP粒径越小,颗粒团聚粒径和团聚速度越小,其原因可能是ZrP碟片的粒径越小,相同质量浓度条件下碟片数目浓度越大,对TiO_2的空间位阻作用越强。     

热处理温度对纳米ITO粉体形成的影响

纳米ITO粉体是光电材料中很重要的的基础材料。文章主要研究了水相共沉淀法制备ITO粉体过程中,热处理温度对粉体形成过程的影响,并用TG—DTA、TEM和XRD对其作了表征分析。结果表明,ITO前驱体在320℃以上发生晶型转变成ITO粉体,并随着温度的升高,粉体晶粒长大。在700℃左右,晶粒粒径最小,比表面积最大,团聚系数最小,粒径分布均匀,单分散性能好,无团聚现象。温度过高时,因烧结现象的发生,可能产生硬团聚。     

介晶半导体材料的合成及应用研究进展

传统半导体纳米材料大部分为多晶结构或单晶结构。而介晶是一类由初级纳米颗粒以结晶学有序的方式自组装而成的纳米粒子超结构,具有类似单晶的原子结构和散射特征,既保留着初级纳米颗粒的晶界,又表现出强烈的各向异性,从而具有与多晶和单晶均不同的独特结构与性能。例如,介晶结构中的初级纳米颗粒以一定的方式相互连接,与无序堆积的多晶相比,具有极高的结晶性,甚至接近单晶,能够有效减小载流子在材料内部的复合概率;初级纳米颗粒之间的晶界并未完全消失,存在一定的空隙,具有较高的空隙率和比表面积以提供更多的活性位点;初级纳米颗粒在定向吸附过程中有序地取向排列,暴露出高能晶面,显著提高了其反应活性。金属氧化物半导体材料在光催化、电化学和气敏等领域应用广泛,其反应机理均是发生在材料表面的气-液、气-气、气-固反应,因而均需要材料具有大的比表面积和较高的表面活性。而介晶结构是以纳米颗粒作为基本构筑单元的非经典结晶产物,具有比表面积大、孔隙率高、表面活性高等优点,有望获得远超过传统材料的优异性能,因此近年来介晶结构金属氧化物半导体的制备成为了研究热点。研究者们基于物理或者化学驱动的纳米架构自组装过程,通过改进传统制备工艺,如水热法、溶剂热法、离子热法等,成功调控纳米材料成核、生长的方式,制备出具有介晶结构的TiO_2、ZnO、CuO、SnO_2等半导体材料,并且通过优化制备工艺,可以调节材料的比表面积、孔隙率和表面活性。进一步分析介晶结构与性能的构效关系,对推广介晶结构材料的应用具有重大的指导意义。但是目前介晶的研究还处于起步阶段,各种组分、形貌和结构的介晶的合成、结晶理论的基础研究以及材料的应用开发都还有待进一步探索。本文归纳了介晶半导体材料的研究进展,包括制备方法及不同制备方法所获得材料的特征及优缺点;介绍了半导体介晶材料在光催化性能、电化学性能和气敏性能等领域的应用现状,总结了介晶结构与性能的构效关系,对介晶结构的发展方向进行了展望并指出了其面临的问题。     

纳米水滑石的制备、特性及应用

水滑石是一种层状双羟基阴离子粘土,由金属离子与6个羟基构成的八面体共边组成,是一类具有层状结构的新型无机材料,其八面体层状结构中部分M2+被M3+同晶取代而使层板带正电荷,层间充填的阴离子起平衡电荷作用.此结构决定了水滑石具有碱性、层板上阳离子可调配性、层间阴离子可交换性三大特性,可作为酯交换和氧化还原催化剂以及催化荆载体,广泛应用于吸附、离子交换、合成材料、日用化工、催化、超导以及环境保护等方面.综述了纳米水滑石的特性、制备方法及应用,为实现纳米水滑石的产业化低成本生产及应用奠定了基础.     

纤维素基金属纳米粒子复合催化剂的制备与应用

纤维素是一种来源广泛、比表面积大、多羟基且环境友好型的生物高分子材料,其水悬浮液可形成三维网络缠结结构,从而为具有催化活性的金属纳米粒子提供负载位点,使其均匀分散并固定于基底内部或表面构建复合催化剂材料,进而有效提高催化性能.本文综述了纤维素基金属纳米粒子复合催化剂的制备及应用的相关研究,重点介绍了不同纤维素基材料作为...     

超细CeO2粉体在醇水混合介质中的超声分散行为

通过测定20nm、200nm、500nm和5μmCeO2粉体在醇水混合介质中的粒度分布、表面电性及分散稳定性,研究了不同粒径级别超细CeO2粉体在体积比为1∶1的醇水系悬浮液中的超声分散行为。实验结果表明:在一定超声功率和超声频率下,不同粒径级别醇水系CeO2悬浮液均存在最佳超声时间。不同粒径级别醇水系CeO2悬浮液的表面电性各不相同;纳米级和亚微米级CeO2在醇水中所带Zeta电位为正值,微米级CeO2的Zeta电位为负值,悬浮液中CeO2粉体的平均粒度越大,其电位绝对值越小。不同粒径级别醇水系CeO2悬浮液的分散稳定性能各不相同;从超声结束后的分散效果来看,亚微米CeO2粉体在醇水混合介质中的分散性能最好;从多个沉降时间段内的稳定性来看,纳米CeO2粉体在醇水混合介质中的稳定性能最好。     

单分散纳米SiO_2微球表面化学修饰及STF效应研究进展

溶胶-凝胶法制备纳米SiO2的分散性好、粒径可控,但由于纳米颗粒的比表面积大,容易团聚。因此可以通过化学方法对其进行表面化学修饰以改善其分散性,提高应用领域。本文主要介绍了溶胶-凝胶法制备单分散纳米SiO2微球,表面化学修饰的化学方法及剪切增稠(STF)效应研究进展。     

纳米碳材料的功能化及其在电极修饰中的应用

纳米碳材料因具有比表面积大、电导率高和良好的化学稳定性等特点而用作电极的修饰材料。但使用过程中存在与水或有机相相溶性欠理想、分散不均匀和易团聚等缺陷。综述了共价键和非共价键修饰、掺杂无机金属纳米颗粒等改性方法以及改性后的纳米碳材料对修饰电极性能的影响。     

溶胶水解初始条件对TiO2纳米颗粒性质的影响

对溶胶水地制备TiO2纳米颗粒的初始条件进行了研究，发现初始反应液在中性、碱性和酸性条件下，均能制备出纳米级TiO2颗粒。本文从晶型、平均粒径、比表面积、在水中的分散性和光催化氧化苯酚的性能几方面，讨论了反应初始条件对TiO2纳米颗粒性质的影响。     

超声方式和分散时间对注射成形用铁、镍粉末粒度测量的影响

利用激光衍射法对注射成形用铁、镍原材料粉末进行粒度测量，分别从超声方式和超声时间上对测量条件进行研究。结果表明，对铁粉，宜在大功率超声装置上将样品分散15min后进行测量；对于镍粉，宜在大功率超声装置上将样品分散30min后进行测量。     

煅烧温度对二氧化钛纳米晶性能的影响

研究了不同煅烧温度下,锐钛矿相、混晶和金红石相二氧化钛纳米晶的 粒径、比表面积和吸收光谱的变化。经相同的温度煅烧后,金红石相二氧化钛纳米晶的生长速率和比表面积下降速率均大大高于锐钛矿相,表明高温反应或煅烧难以获得金红石相纳米晶,真空热处理的金红石相二氧化钛纳米晶可以保持较高的比表面积和较小的粒径,但易导致非化学配比、晶格缺陷并降低了粉体的性能。     

Comparative study of ground and sonicated vermiculite

The aim of this work is to compare the effects of grinding and ultrasonic treatment on vermiculite. Sonication produces a drastic change in particle size (mass median particle diameter 2.4 μm, layer thickness 38 nm), while the resulting material is crystalline as assayed by X-ray diffraction patterns. The TEM study shows that the sonicated vermiculite consists of nanometric flakes. On the other hand, grinding produces particles with medium diameter in the range of about 9 μm and very broad particle size distribution. X-ray and TEM studies of ground sample show an important alteration with grinding time. Prolonged grinding of vermiculite produces the loss of long-range order and eventually an amorphous product is obtained. The results show that grinding treatment produces a decrease of particle size, amorphization and agglomeration of the particles, whereas the ultrasound treatment only produces a decrease of particle size.     

改性干燥法制备纳米氧化镁粉体的研究

以六水氯化镁和尿素为原料,采用均匀沉淀法制备出氢氧化镁沉淀,利用不同改性干燥法除去沉淀中的湿分,再将干燥的氢氧化镁粉体经马弗炉煅烧得到纳米氧化镁粉体,通过透射电子显微镜和X射线衍射仪的表征与分析,研究了改性干燥方式对纳米氧化镁粉体形貌、颗粒尺寸和团聚情况的影响,讨论了改性干燥的基本原理和改性剂的作用。研究结果表明,改性干燥方式对纳米氧化镁颗粒形貌和大小的影响不大,对其颗粒间团聚状态影响很大。     

Mechanical treatments on design powder ceramic materials: Insight into the textural and structural changes

Mechanical treatment of porous ceramics, such as porous clay minerals, is a crucial step in ceramic processing. Among clay minerals, design swelling brittle micas have shown exceptional properties for further applications, although they exhibit low surface area and porosity. But, their mechanical activation could improve their textural properties and deserves to be investigated. Thus, the aim of this work was to evaluate the effects of gradual grinding in their surface and framework. At short grinding times, the surface area increases and mesoporous and microporous are generated. Long grinding time provokes particle agglomeration with the consequent change in their colloidal stability. At bulk level, framework defects are observed in both tetrahedral and octahedral sheets and increase with the total layer charge.     

Dry dispersion of fine particles in gaseous phase

Dry dispersion of fine particles is discussed as a simultaneous process of dispersion and agglomeration. Various problems on the dry dispersion are summarized based mainly on our works and key terms such as partial dispersion efficiency and powder characteristic value are reviewed to analyze the dispersion mechanism and to evaluate easiness of dispersion for any kind of powder. Improvement of disperser unit is also suggested based on the analysis of dispersion process.Electrostatic charging, especially contact electrification between particle and its surface layer, seems to give further improvements on the dry dispersion of fine powder containing sub-micron particles.     

超细煤粉的静电分散研究

为了解决超细煤粉加工和利用过程中的聚团问题,提高煤粉的附加值和功能化利用,本文中采用正交试验的方法研究了静电分散对超细煤粉的分散效果及其主要影响因素,并用高精度粒度分析仪对静电分散前后粒度进行了检测。实验结果表明,静电分散后的粒度明显变小,静电分散作用可保持7d左右。静电分散方法能有效分散空气中超细煤粉的聚团。     

Aerosol Synthesis of Inhalation Particles via a Droplet-to-Particle Method

ABSTRACT

Inhalation powders with consistent particle properties, including particle size, size distribution, and shape were produced with an aerosol synthesis method. Compared to conventional spray drying, the aerosol method provides better control of the thermal history and residence time of each droplet and product particle due to the laminar flow in the heated zone of the reactor where the droplet drying and particle formation take place. A corticosteroid, beclomethasone dipropionate, generally used for asthma treatment was chosen as a representative material to demonstrate the process. Spherical particles were produced with a droplet-to-particle method from an ethanolic precursor solution. The droplets produced with an ultrasonic nebulizer were carried to a heated zone of the reactor at 50–150°C where the solvent was evaporated and dry particles formed. The mass mean diameter of the particles were well within the respirable size range (approximately 2 μm). The geometric standard deviation (GSD) of produced particles was approximately 2. The particle surface structure varied from smooth to rough depending on the degree of particle crystallinity and was affected by the thermal history of the particle. Amorphous particles with smooth surface were most likely obtained due to the rapid evaporation of the solvent from the droplet combined with the slow diffusion of the beclomethasone dipropionate molecule. The amorphous particles were transformed slowly to crystalline particles in the open atmosphere. In addition, the particle surface structure changed from smooth to rough during storage. The process was accelerated by thermal post-annealing. However, additional heating also increased particle sintering. By optimizing the reactor parameters, and thus increasing the molecular diffusion, stable, crystalline particles were produced at 150°C.     

Potassium chloride caking tendency: A parametric study of cake break energy

Undesired particulate agglomeration can create powder flow issues during manufacturing. Potassium chloride (KCl), a commercial product used in powder form as a potassium source, is known to agglomerate. The main objective is to develop a method to assess KCl agglomeration, then use it to understand its driving forces and the phenomena taking place. Based on industrial data in pharmaceutical manufacturing, the following 5 parameters are considered as critical in terms of agglomeration: conditioning humidity, conditioning time, drying, applied pressure and particle size. Beakers containing 40?g of original or ground KCl powder are compacted under specific humidity conditions in a bell jar. Once the beakers are conditioned, agglomerate hardness tests evaluate agglomeration extent by correlating it with the energy required for powder penetration. This energy is calculated from force-distance curves. The results show that the Area Under the force vs distance Curve (AUC) is a good indicator of agglomeration extent. Thus, the AUC is a scalar and has units of work. Based on AUC analysis, the highest agglomeration is found in conditioning humidity of 85% relative humidity (RH), original particle size, drying and conditioning time of 16?h. The agglomeration of original versus ground particle size powders is further investigated over time in a conditioning test. Preliminary tests validate our method and indicate that KCl premixing with other materials can solve agglomeration problems encountered during manufacturing processes as KCl-particle-particle interactions per unit volume are reduced.     

Aerosol Synthesis of Inhalation Particles via a Droplet-to-Particle Method

Inhalation powders with consistent particle properties, including particle size, size distribution, and shape were produced with an aerosol synthesis method. Compared to conventional spray drying, the aerosol method provides better control of the thermal history and residence time of each droplet and product particle due to the laminar flow in the heated zone of the reactor where the droplet drying and particle formation take place. A corticosteroid, beclomethasone dipropionate, generally used for asthma treatment was chosen as a representative material to demonstrate the process. Spherical particles were produced with a droplet-to-particle method from an ethanolic precursor solution. The droplets produced with an ultrasonic nebulizer were carried to a heated zone of the reactor at 50-150°C where the solvent was evaporated and dry particles formed. The mass mean diameter of the particles were well within the respirable size range (approximately 2 μm). The geometric standard deviation (GSD) of produced particles was approximately 2. The particle surface structure varied from smooth to rough depending on the degree of particle crystallinity and was affected by the thermal history of the particle. Amorphous particles with smooth surface were most likely obtained due to the rapid evaporation of the solvent from the droplet combined with the slow diffusion of the beclomethasone dipropionate molecule. The amorphous particles were transformed slowly to crystalline particles in the open atmosphere. In addition, the particle surface structure changed from smooth to rough during storage. The process was accelerated by thermal post-annealing. However, additional heating also increased particle sintering. By optimizing the reactor parameters, and thus increasing the molecular diffusion, stable, crystalline particles were produced at 150°C.